Carpet manufacturers generally want to see professional hot water extraction every twelve to eighteen months, and many warranties quietly depend on it. That number assumes an average household. Most of the houses we walk into are not average.
The honest test is the traffic lane. Look at the path from your front door to wherever people sit, in daylight, from a low angle. If that path is visibly a different shade than the carpet two feet to either side, the base of the pile is loaded with soil and a vacuum is no longer reaching it. That is the point where cleaning stops being cosmetic and starts being maintenance, because dry soil is abrasive and it cuts the fiber every time somebody walks on it.
Pets and kids move the schedule up to roughly every six to nine months, and not only because of accidents. Dander and body oil work down into the pile, hold onto odor, and attract more soil. Northern Illinois adds its own factor: five months of salt, slush, and road grit tracked in from November through March, which is why a lot of our residential extraction work happens in early spring.
In between professional visits, the single highest-value thing you can do is vacuum slowly. Most people push the machine far too fast for the beater bar to do anything. Two or three passes over traffic areas, at walking pace or slower, pulls out dry soil before it gets ground down to the backing.
One more thing worth knowing: carpet that gets cleaned regularly comes back better every time. Carpet that gets ignored for five years often cannot be fully recovered, because the fiber itself is worn, not dirty. We will tell you which one you have before we quote it.